Case report: a missed case of chronic Q fever infective endocarditis demonstrating the ongoing diagnostic challenges

Diagnosis of chronic Q fever is often difficult for clinicians, particularly in the presence of a second pathology. In addition to the chronic constitutional symptoms, the most common manifestations of chronic Q fever include infective endocarditis and endovascular infection. We describe a case of prosthetic valve infective endocarditis caused by both Streptococcus sanguinis and Coxiella burnetti on a background of a previous aortic graft and bioprosthetic aortic valve replacement 2 years earlier. The diagnosis of chronic Q fever infective endocarditis was delayed because the significance of the abnormal valve histology from the patient's previous surgery was initially overlooked. It was only after the patient had relapsed on appropriate therapy for the S. sanguinis prosthetic valve endocarditis that a subsequent review of the operative valve histology, along with the patient's epidemiological risk factors, led to consideration of an additional culture-negative cause for infective endocarditis. Histological examination of the valve tissue had shown exophytic fibrin vegetations and acute inflammation. Further clinical assessment revealed previous exposure to Q fever and C. burnetti DNA was detected via polymerase chain reaction on the valve tissue. Q fever infective endocarditis must be considered if valves are inflamed or have vegetations with a subsequent negative culture. It should also still be considered in the presence of an alternative bacteraemia if the patient has risk factors for exposure.